One conventional optical wavelength-division switching system is described in Japanese patent laid open No. 60-172841 (172841/1985) the laid open date of which is Sept. 6, 1985. The optical wavelength-division switching system comprises an optical variable wavelength filter for demultiplexing a wavelength division multiplexed (WDM) optical signal into a plurality of optical signals each having a wavelength different from others, means for converting the wavelengths of the demultiplexed optical signals in accordance with the specified switching condition, and an optical combiner for combining the optical signals each being of a wavelength different from others.
In operation, the WDM optical signal is supplied from an optical fiber to the optical variable wavelength filter to be demultiplexed into a plurality of the optical signals so that each of the optical signals has a wavelength different from others. The optical signals thus demultiplexed are converted in regard to their wavelengths in the wavelength converting means. For instance, if a wavelength of an optical signal is converted from .lambda..sub.1 to .lambda..sub.2, and that of another optical signal is converted from .lambda..sub.2 to .lambda..sub.1, the optical signals of the wavelengths .lambda..sub.1 and .lambda..sub.2 are switched therein. The optical signals thus converted in regard to their wavelengths are combined in the optical combiner to be supplied to another optical fiber. The optical variable wavelength filter may be, for instance, of a directional coupler type utilizing an electrical-optical effect as described on pages 161 to 163 of "Applied Physics Letters", vol. 33 (2), 1978, or on page 131 of "Applied Physics Letters", vol. 39 (2), 1981, of a mode conversion type as described on page 861 of "Applied Physics Letters", vol. 40 (10), 1982, or of such a means as utilizing an acoustic-optical effect.
Much attention is paid to such an optical wavelength-division switching system as described above because a scale of line capacity can be expanded for the reason that a characteristic of light is effectively utilized therein as compared to a space-division switching system or time-division switching system.
In the optical wavelength-division switching system, however, the number of wavelength channels is limited to some extent insofar as such a variable wavelength filter as described above is adopted therein.
Further, a characteristic of crosstalk is prevented from being improved for the same reason.
In a practical use, the optical wavelength-division switching system can not be applied to an optical communication system including wavelength channels of several tens to one hundred.